1. Field of the Invention
The present invention relates generally to air filtering mediums for small particulate matter, and more particularly to single-layer, non-entraining, air filtering mediums which may be used without a mechanical forced-air ventilation system.
2. Description of Related Art
Air filtering systems for removing deleterious particulate matter are important for general health reasons and are particularly important for persons having allergies, asthmatic conditions and the like. Ventilation of interior spaces is also important for the removal of dampness and airborne chemicals, such as phenols escaping from drapes, furniture, etc.
Small particulate matter and allergenic pollens are usually larger than 15 microns, with most above 20 microns in diameter. Particles in smog range down to 0.01 microns. Air ventilation systems in buildings generally include air filters that require mechanical blowers and other large equipment to force air through the filtering media. These types of filters are designed to remove only large dirt and dust particles and do not remove the small particulate matter discussed above.
It would be desirable to have a physical air filtering medium having openings small enough to effectively filter small particulate matter and allergenic pollens. In particular, it would be desirable to have a non-entraining air filtering system for small particulate matter and allergenic pollens that can be used in non-forced-air (natural) ventilating conditions. As used herein, "non-forced-air natural ventilating" means the movement of air without the use of mechanical blowers or the like.
Another type of air filtering system is the "High Efficiency Particulate Arrestor" (HEPA). These are usually mat type media and require mechanical forced air in order to push air through the filtering medium. They are usually used in units which recirculate interior air.
Air filtering systems designed to remove small particulate matter usually include built-up or blown mat filters that require mechanical forced-air blowers. They function by capturing or collecting the particulate matter on or in the built-up mat filter. As a result, the filter efficiency declines as the filtering medium becomes clogged with particulate matter. Thus, air filters of this type must be periodically cleaned or replaced. Where the air is heavily contaminated with particulate matter, such air filters must be cleaned or replaced quite often. U.S. Pat. Nos. 570,219; 1,056,722; 2,478,097 and 4,022,596 disclose air filtering systems of this type. U.S. Pat. Nos. 2,551,175 and 2,615,477 disclose liquid filtering systems which function by entraining or collecting small particulate matter.
U.S. Pat. Nos. 4,728,349, 4,904,288 and 5,037,455 disclose multi-layered air filters which function by entraining or capturing particulate matter and which utilize mechanical forced-air ventilation to move air through the filter. U.S. Pat. Nos. 4,728,349 and 4,824,451 disclose non-woven, blown mat-type filtering mediums which also require mechanical forced-air.
Other types of air filters are suitable for being mounted in a window frame. For example, U.S. Pat. No. 3,675,402 shows a sliding window air filter assembly utilizing a multilayer filtering medium. This air filter assembly must be cut down to the size of the window opening. Once the frame has been cut, it cannot subsequently be widened.
The key elements for an air filtering medium to prevent entry of small particulate matter in non-forced-air ventilating systems are: (1) the openings in the filtering medium must be sufficiently small enough to prevent the passage of the particulate matter; and (2) the surface-area of the filtering medium must be sufficiently open that a pressure differential across the filtering medium is low enough to permit natural, non-mechanical ventilation.
New processes in material manufacturing, such as microfilament weaving, micro-laser cutting, chemical and photo-etching, x-ray lithography, stretching of microporous sheets, and the like, make it possible to construct a single-membrane filtering media with sufficiently small openings to prevent the passage of small particulate matter and with sufficient openness to provide a low differential pressure across the filter to gain natural ventilation without the necessity of mechanical blowers. Such a filtering media would be particularly useful mounted in an adjustable frame that can be selectively disposed in an opening such as a window. Using smaller and smaller openings, even down to approximately 0.01 microns, in a membrane with sufficient openness, would restrict particles such as those found in industrial smog, while still permitting natural ventilation.
One object of the present invention is to provide an air filtering means which prevents the passage of small size particulate matter without collecting the particulate matter in or on the filtering medium.
Another object of the present invention is to provide an air filtering means that permits natural ventilation, i.e. air flow under low differential pressures without the necessity of forced-air ventilation, but which may also be used with a mechanical blower.
A still further object of the present invention is to provide an air filter system that is self-cleaning and thereby eliminates or substantially reduces the need for short term replacement or cleaning.
Another object of the present invention is to provide an adjustable frame in which the filter medium can be selectively adjusted to varying size openings such as windows.